Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $48.98   6.461%   $52.1446   $52.14   $52.15   $52.10  
  Purchase #2 $150.29   4.847%   $157.5746   $157.57   $157.55   $157.60  
  Purchase #3 $100.42   12.841%   $113.3149   $113.31   $113.30   $113.30  
  Purchase #4 $153.34   12.211%   $172.0643   $172.06   $172.05   $172.10  
  Purchase #5 $229.74   5.307%   $241.9323   $241.93   $241.95   $241.90  
  Purchase #6 $147.96   11.142%   $164.4457   $164.45   $164.45   $164.40  
  Purchase #7 $23.87   8.491%   $25.8968   $25.90   $25.90   $25.90  
  7 purchase totals = $854.60       $927.3732   $927.36   $927.35   $927.30